Opiate dependence is a severe and costly societal problem. While methadone maintenance (MM) is effective for managing this disorder, as many as 70% of MM clients are interested in detoxification in order to achieve a drug-free life. To date, however, success rates for opiate detoxification are very low, in part, due to physical and psychological symptoms and fears associated with opiate withdrawal. Few behavior therapies have been developed to promote abstinence during and subsequent to opiate dose reduction and even fewer treatment models have devoted sufficient attention to the distressing experiences specific to methadone withdrawal. A novel behavioral treatment, Acceptance and Commitment Therapy (ACT) is based on the idea that attempts to avoid private experience (thoughts, feelings, memories, bodily sensations) are ubiquitous yet often pathogenic. Given that opiate dependent individuals in detoxification often resort to opiate use to reduce, escape or avoid commonly experienced fear, anxiety, and physical symptoms, ACT seems uniquely applicable to the opiate detoxification experience. By decreasing experiential avoidance during dose reduction, ACT has the potential to significantly increase methadone detoxification success rates. The proposed Stage I research will develop and test an innovative ACT-based opiate detoxification behavioral therapy within the context of a long-term methadone dose reduction program. In Phase 1, investigators will develop the new therapy based on previous ACT protocols, focus groups, and expert knowledge. Phase 2 will consist of a pilot trial to evaluate the ACT-based opiate detoxification therapy. A randomized, controlled, between groups design will be used in which opiate dependent patients (N=70) motivated for detoxification are assigned to one of two treatment conditions: ACT or Drug Counseling. A 4-week stabilization period will precede a 5-month dose reduction period using an inverse exponential dosing strategy, with 1-month follow-up. Behavioral treatments will consist of 24 weekly sessions beginning in stabilization. Specific aims are to test the feasibility and acceptability of ACT for opiate detoxification, to assess patient improvement (e.g., drug use, HIV/Hepatitis C risk behavior, psychosocial functioning), to generate sufficient data to provide a basis for a power analysis, and to evaluate the active mechanisms of change in ACT: experiential avoidance as a mediator of treatment effects and a moderator of the impact of withdrawal symptoms, negative affect and detoxification fear. The work will be conducted using the rigorous procedures of our Treatment Research Clinic (SARC, UT-Health Science Center- Houston) in collaboration with experts in behavior therapy development and the originators of ACT. The research will contribute both theoretically and empirically to a rather sparse literature concerning effective behavior therapy for opiate detoxification. Effective treatment provided in conjunction with detoxification from agonist medication could result in significant decreases in the substantial health and social costs associated with chronic opiate dependence.